<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>圆形</title>
</head>
<body>

<canvas id="myCanvas" width="200" height="100" style="border: 1px solid #c3c3c3;">
  Your browser does not support the canvas element.
</canvas>

<script type="text/javascript">
  var c = document.getElementById("myCanvas");
  var cxt = c.getContext("2d");
  cxt.fillStyle = "#FF0000";
  cxt.beginPath();
  cxt.arc(70,18,15,0,Math.PI*2,true);
  cxt.closePath();
  cxt.fill();
</script>

</body>
</html>